In a related art, machine tools are known which perform machining such as cutting by moving a tool relative to a workpiece. Among such machine tools, numerically controlled machine tools are known which are configured to set a tool path based on coordinates or the like of a predetermined feed axis and perform machining while moving the tool relative to the workpieces. Such machine tools are capable of performing machining automatically while changing relative position of the tool with respect to the workpiece by moving at least one of the workpiece and the tool in accordance with a command from a control device.
The machine tools form workpieces having target shape by performing machining on workpieces having a predetermined shape. A machining program for operating the machine tools can be generated automatically based on target shapes of designed workpieces by a CAM (Computer Aided Manufacturing) apparatus. The CAM apparatus generates a tool path including information on relative movement of the tool with respect to the workpiece based on the target shape of the workpieces. Subsequently, the machining program including the information on the tool path is outputted.
The machine tool sets movement points at predetermined intervals based on the machining program, and controls the tool so as to pass through the movement points. For example, when the workpiece stops and the tool moves, the tool moves in such a manner that a tool tip point passes through the movement points. The tool path includes the movement points, and the tool moves linearly between the movement points.
When a surface of the workpieces having the target shape is a curved surface, the tool path follows the surfaces of the workpieces. However, since the tool moves linearly between the movement points, machined surfaces may not become smooth curved surfaces and pointed portions formed by combining flat plains may be formed on portions of the workpieces which are to be curved surfaces. Accordingly, in a technique of the related art, smoothing treatment is known which corrects a tool path in order to achieve workpieces having smooth machined surfaces. Smoothing treatment is known to correct positions of the movement points on the tool path so as to generate a new tool path.
International Publication No. 2012/056554 discloses a tool path generation method including a procedure of calculating bent angles at bent points of a bent line that is formed by connecting machining points in line in sequence and a procedure of deriving an approximate curve that generates an approximate curve that gets closer to the bent point as the bent angle increases. In the tool path generation method, generation of the tool path along the approximate curve is disclosed.
Japanese Patent No. 3958112 discloses in the specification a velocity control method by using a numerical control device, which smooths command data having a curved shape approximated by segments and corrects the command point by a unit smaller than set unit with a predetermined tolerance. It is disclosed that in this velocity control method, a velocity control is performed by using the corrected command point and computing a velocity in which accelerations of respective movement components are specified values or less.